1. Field of the Invention
The present invention relates to high-frequency modules that include a substrate on which a non-reciprocal circuit element is mounted.
2. Description of the Related Art
To date, non-reciprocal circuit elements such as isolators and circulators have been employed in high-frequency modules such as power amplification modules of transmission circuit sections of communication terminals such as cellular phones and wireless LAN devices, by utilizing their characteristic of transmitting a signal in only a specific predetermined direction (for example, refer to Japanese Unexamined Patent Application Publication No. 2011-199602 (paragraphs 0025 to 0045, FIGS. 1, 2, 4 to 8 and so on)). As illustrated in FIG. 5 and FIG. 6, a non-reciprocal circuit element 100, which is mounted in a high-frequency module, includes, for example, a rectangular-parallelepiped-shaped ferrite 101, on which central electrodes 103 and 104 are provided, and a pair of permanent magnets 102 and is formed by sandwiching the ferrite 101 between the pair of rectangular-parallelepiped-shaped permanent magnets 102 such that a direct-current magnetic field B is applied to the ferrite 101.
The ferrite 101 has a rectangular parallelepiped shape having a pair of opposing main surfaces, is provided with a first central electrode 103 and a second central electrode 104, which are in a state of being insulated from each other, on its two main surfaces, and is provided with an input terminal 105, an output terminal 106 and a ground terminal 107 arranged in a straight line on a bottom end surface thereof. In addition, in order to decrease the size and profile of the high-frequency module, the non-reciprocal circuit element 100 is mounted on a substrate 2 without a yoke for preventing the direct-current magnetic field B of the permanent magnets 102 from leaking to the outside.
That is, the non-reciprocal circuit element 100 is mounted on the substrate 2 by respectively soldering the input terminal 105, the output terminal 106 and the ground terminal 107 using, for example, reflow soldering, to mounting electrodes 2a to 2c arranged in a straight line on the substrate 2, which is included in the high-frequency module. In addition, chip-like components 3 such as capacitors and resistors for adjusting the characteristics of the non-reciprocal circuit element 100 are respectively mounted on mounting electrodes 2d to 2h on the substrate 2 of the high-frequency module and the various components mounted on the substrate 2 are electrically connected to each other through wiring line electrodes provided on the substrate 2. By forming the non-reciprocal circuit element 100 in this way, the high-frequency module can be reduced in size and profile when compared to the structure of a high-frequency module in which a non-reciprocal circuit element, which is formed by arranging a ferrite having a copper wire wound therearound as a central electrode between a pair of permanent magnets, is mounted. FIG. 5 illustrates an example of a non-reciprocal circuit element and FIG. 6 is an exploded perspective view of the non-reciprocal circuit element of FIG. 5.
As has been described above, in the non-reciprocal circuit element 100, the terminals 105 to 107 provided on the lower end surface of ferrite 101 face the substrate 2 and are respectively connected to the mounting electrodes 2a to 2c of the substrate 2 via solder. There are sometimes variations between the thicknesses of the terminals 105 to 107 on the lower end surface of the non-reciprocal circuit element 100 due to the problem of the precision with which the terminals are formed. Consequently, there is a risk of the non-reciprocal circuit element being mounted on the substrate 2 in a tilted state. Therefore, when mounting the non-reciprocal circuit element 100 on the substrate 2, it is preferable that the amount of solder applied to each of the terminals 105 to 107 be finely adjusted, but in actual practice, it is difficult to finely adjust the amount of solder applied to each of the terminals 105 to 107 and there is a risk of the terminals 105 to 107 being short-circuited due to melted solder and of connection defects occurring between the terminals 105 to 107 and the mounting electrodes 2a to 2c due to there being too much or too little solder. In addition, there is a risk of the non-reciprocal circuit element being tilted on the substrate 2 depending on the amounts of solder.
Therefore, since the non-reciprocal circuit element 100 is mounted on the substrate 2 with its lower end surface on which the terminals 105 to 107 are provided facing the substrate 2, the connection states between the terminals 105 to 107 and the mounting electrodes 2a to 2c cannot be visually checked after the non-reciprocal circuit element 100 has been mounted on the substrate 2. In addition, when the non-reciprocal circuit element 100 is mounted on the substrate 2, it is necessary to match the impedances between the wiring line electrodes and electronic components provided on the substrate 2 and the non-reciprocal circuit element 100, and modifying the designs of the wiring line electrodes and the electronic components provided on the substrate 2 in accordance with the individual characteristics of non-reciprocal circuit elements 100, among which variations occur at the time of manufacture, in order to adjust the impedances is not realistic.
In addition, the terminals 105 to 107, which are connected to the mounting electrodes 2a to 2c of the substrate 2, are arranged in a straight line on the lower end surface of the ferrite 101 and therefore there is a risk of the non-reciprocal circuit element 100 being not well balanced in a mounted state on the substrate 2 and of the non-reciprocal circuit element 100 being fixed to the substrate 2 in a tilted state due to variations in the amounts of solder.